1. Field of the Invention
This invention relates to an electrophotographic method using a single layer organic photosensitive material, and more specifically to an electrophotographic method in which a decrease in the surface potential of the photosensitive material at the time of repeated use is suppressed.
2. Description of the Prior Art
In electrophtography, a photosensitive material is charged to a fixed polarity, the charged photosensitive material is imagewise exposed, the resulting electrostatic latent image is developed with a toner, and the toner image is transferred to a transferring paper to form an image. Since an untransferred toner remains on the photosensitive material after the transferring of the toner, it is cleaned by an elastic plate, and furthermore, to eliminate the remaining charge on the photosensitive material, charge elimination is performed by exposure on the entire surface. Accordingly, the above process is repeatedly carried out.
Various types of photosensitive materials used in electrophotography are known such as a selenium photosensitive material, an amorphous silicon photosensitive material (a-Si) and organic photosensitive materials (OPC). The organic photosensitive materials are suitable for electrophotography of a digital type using a laser light in spectral sensitivity and cost.
Roughly classified, the organic photosensitive materials include a laminated photosensitive material obtained by laminating a charge generating agent layer (CGL) and a charge transporting agent layer (CTL), and a single layer photosensitive material prepared by dispersing a charge generating agent (CGM) and a charge transporting agent (CTM) in a resin. The former has high sensitivity but contains a complicated layer construction and is high in production cost. The latter has the defect that its layer construction is simple, but escape from the charge at the time of exposure is not good (the sensitivity is somewhat low).
It is already known to use a light of a light-emitting diode (LED) for elimination of a charge from a photosensitive material. As a charge eliminating light, light rays of a wavelength to which a photosensitive material has sensitivity are generally used.
For example, Japanese Laid-Open Patent Publication No. 259175/1991 discloses a charge-eliminating apparatus which is used in an electrophotographic copying machine using a photosensitive drum having sensitivity to a red light, which is characterized in that a light-emitting diode which emits light in a long wavelength side of a wavelength region to which the photosensitive drum is sensitive is used as a light source.